Ophthalmic instrument



June 30, 1936.

c. E. FERREE ET 2,045,704

OPHTHALMIC INSTRUMENT ,Filed March 25, 1933 2 Sheets-Sheet l R l 55 J 44s 72 T CLARENCE ERROL FERREE GERTRUDE RAND FERREE INVENTORS 47 29 BY mv 70 FIG.8 36 73 ATTORNEY June 30, 19.36. c. E. FERREE ET AL OPHTHALMICINSTRUMENT Filed March-25', 1953 2 Shets-Sheet '2 CLARENCE ERROL FERREEiiiii 111$:

Il-lllll GERTRUDE RAND FERREE iNVENTORS %4 ATTORNEY Patented June 30,1936 UNITED STATIC-1S OPHTHALMIC INSTRUMENT Clarence Errol Fence andGertrude Band Fm,

Baltimore, Md.

Application March 25, 1933, Serial No. 662,743 11 Claims. (01. 88-20)This'invention relates to ophthalmic instruments and more particularlyit has reference to such types of instruments as are used for testing,measuring or checking the light and color senses as well as the light,dark and color adap- Still another object is to provide an instrument ofthe type described in which all of the light in the test and/orpre-exposure fields can be measured and directed into the eye undertest. A further object is to provide an instrument of the 'typedescribed having means whereby acuity can be tested, over a wide rangeof illumination, in-

dependent of the refractive system of the eye. Other objects are toprovide in an instrument of the type described a viewing aperture ofsubstantially one and a half millimeters in diameter;

a single light source for illuminating the test and/or pre-exposurefields; independent means for varying the illumination on the testand/or pre-exposure fields and means for indicating the illumination inthe fields; diaphragm means for to selectively providing various testfields; and

means for checking the intensity of the light source. Other objects andadvantages reside in certain novel features of construction, arrangementand combination of parts as will herein- 85 after be more fullydescribed and pointed out in the appended claims.

Referring to the drawings:

Fig. 1 is a perspective view of an instrument embodying our inventions.40 Fig. 2 is a vertical sectional view taken through the casing of theinstrument.

' Fig. 3 is a sectional view taken on line 3-3 of Fig. 2. a

, Fig. 4 is a sectional view taken on line 4-4 of 45 Fig. 2.

Figs-5 and 6 are fragmentary detail views showing the scale means forindicating the intensity of illumination.

Fig. '7 is a sectional view showing our checking 50 standard in positionon the instrument.

Fig. 8 is a schematic view of a modified form of optical system.

A preferred embodiment of our invention is illustrated in the drawingswherein I! indicates 5 the supporting. base which is preferably formedfilters 40 of different densities.

of a single casting. The housing, indicated generally at It, is mountedin fixed angular relation to a rod H which is slidably mounted in baseii for vertical adjustment and adapted to be secured in adjustedposition by-means of a clamping. screw, not shown, operated by knob ill.The base l5, has a forwardly projecting portion I 9 on which a chin rest20 is mounted for vertical and angular adjustments. 0

The housing l6 comprises a front casing por- 10 tion 2| and a rearcasingportion 22 both secured to an intermediate member 23. Movablymounted within casing 22 is tubular member 24 having a rack portion 25cooperating with a rotatable pinion 25 which can be turned by knob 26'so 15 as to move the tubular member 24 back and forth within casing 22;The tubular member 24 is closed at one end by a plate 21 carrying asupport 28 on which a light source, such as the incandescent lamp 29, ismounted. The upper 20 side of the tubular member 24 is provided with aslot 30 which is covered by a translucent scale member 3i. In the top ofcasing 22 there is provided an opening 32 having a fixed index 33 whichcooperates with the trans-illuminated 5 scale 3| to indicate theposition of the lamp 29 for a purpose to be hereinafter described.

The' intermediate member 23 is provided with a wall 34 having acentrally disposed opening 35 in which is mounted a diffusion disk suchas 30 a plate of opal glass 36. Rotatably mounted on the wall 34, bymeans of screw 31, is a disk 38 having a plurality of spaced openings 39in which are mounted suitable neutral or colored The disk 38 is 5provided with a plurality of circumferentially spaced notches 4| whichare adapted to cooperate with a click spring 42 as the disk is rotatedto selectively position any desired filter in registration with the opalglass 36. Fixedly se- 40 cured to the disk 38 is a translucentcylindrical scale member l3 which is illuminated by lamp 29 so thatnumbers indicating the filter densities can be read through the opening44 in member 23, as will hereinafter be described. 45'

Mounted within casing 2| are the two double convex lenses 45 and 46which cooperate to image the illuminated opal glass 36 at a point whichis slightly beyond the viewing aperture 41 in the concavity 48' ofeye-piece 48 carried at the for- 5 ward part of easing 2 I. Lens 45 actsto collimate the light rays coming from the illuminated opal glass 36and lens 46 serves to focus these rays substantially at the aperture 41'so that an image of the illuminated glass plate 36, which can beregarded as a secondary source, is formed substantially at the pupil ofan eye which is positioned at the eye piece 48. The aperture 41preferably has a diameter of about 1.5 milli meterswhich is less thanthe diameter of the -pupil of the eye and the concavity 48 enables thepatient to place his eye close to the aperture.

This renders the results independent of individual variations in size ofpupil and at the same time independent of the refractive condition ofthe eye.

Rotatably mounted within the casing 2|, directly in front of lens 46, isthe plate 49 having guideways 50 adapted to slidably receive a diaphragmplate provided with a centrally disposed aperture 52 of any desired sizeor shape. A bushing 53 mounted within casing 2i carries spring pressedpin 54 which isadapted to cooperate with the spaced depressions 55 onplate 49 as the latter is turned together with the diaphragm 5| by meansof the knob 56 which projects through slot 5! in casing 2|. Thediaphragm opening 52 can thus be selectively set in a plurality ofangular positions.

In determining the-light minimum, the patient is seated before theinstrument with his eye at the viewing aperture M. The diaphragm plate5! is withdrawn, and the light source 29 and filters adjusted so thatthe patient sees a field completely filled with light. The patient gazesat this field for 3 minutes in order to sensitize the eye to a constantillumination. One of the denser filters 40 is positioned opposite opalglass 36, a field diaphragm 51 is put in place and the lamp 29 is movedrearwardly until the field is no longer visible to the patient. The lamp29 may then be moved forwardly until the field again becomes visible tothe patient. In this manner, it is possible to vary the illumination onthe opal glass 36 so that the test field is just discernible to thepatient. The diaphragm opening 52 may be turned to different angularpositions without knowledge of the patient thereby providing anobjective check on the correctness of the patient's judgment. q

The brightness or amount of light in the field can be determined fromthe transilluminated scales 3| and 43. A suitable calibration curve forthe instrument is determined by actually measuring the light whichpasses out through the aperture 41. The calibration can be made in termsof foot candles or lamberts or any other suitable units. In order toinsure constant performance of the lamp 29, a milliammeter 58 and anadjustable rheostat 59 are arranged in the circuit of the lamp so thatthe lamp can be operated at a predetermined amperage.

In spite of the fact that the lamp 29 can be operated at a certainamperage, it is essential to check the illumination which it producessince the emciency does not always remain constant. In order to do thiseasily and conveniently we provide a checking standard unit which can besubstituted for the eye piece 49 on casing 2| as shown in Fig. '7. Thisunit comprises a casing-69 to which is attached the tube 6! carrying .a

the standard lamp 62 falls on the plate 66 thereby bringing the twofields in juxtaposition to be viewed through the eye piece tube 58. Theintensities of the two fields can thus be compared and any necessaryadjustments made in the cur- 5 rent rate for the lamp 29 in theinstrument. The eye piece tube 68 is provided with an iris diaphragm 68so that a large pre-exposure field or a smaller test field can bequickly provided for a purpose to be hereinafter described. .The innersurface ofthe wall of casing 60 opposite the eye piece tube should havethe same reflecting power as plate 66.

In determining the light difierence the checking standard is positionedon the instrument as shown in Fig. 7. Since the illumination provided bythe standard lamp 52 is known, the operator adjusts the instrument sothat, according to scales 3! and 43, the illuminations of the checkingstandard unit and the instrument are the same. The diaphragm 68 isopened widely so there is provided a relatively large, uniformlymatched, illuminated field which the patient sees upon looking into theeye piece 68. The patient is directed to look at such a matched fieldfor a fixed period of time in order to sensitize the eye. The diaphragm68" is then partially closed so as to provide a small test field and thepatient is directed to move lamp 29 by turning knob 26' until he justnotices that the two portions of the photometric field are of difierentintensities. He

is then directed to move the lamp in the opposite direction until heagain just notices an intensity difl'erenee between the two portions ofthe field. The difference between the scale readings for the match pointand the just noticeable difference point is a measure of the patientslight difiference.

A modified form of the optical system of our instrument is showndiagrammatically in Fig. 8 wherein 29' indicates the light sourceadapted to illuminate a difi'using plate 79. The lens Ii collimates thelight rays and lens 12 focuses them onto a diflusing screen 35'. Lenses35' andtB' cooperate to image the illuminated glass jdiflusing plate 35at a point which is substantially at the pupil of an eye placed ataperture 51. Be-

tween lenses H and 52 there is positioned an iris diaphragm 73 which canbe adjusted so as to vary the intensity of the illumination on plate39'.

From the foregoing'it will be apparent that we are able to attain. theobjects of our invention and provide an instrument which can beconveniently used for testing light and color sense and light, dark' andcolor adaptations. Diaphragms having openings of various shapes andsizes can, of course, be selectively inserted in guideways 50. Adiaphragm having the well known broken circle opening can, for example,be positioned in the guideway 50. With such anobject, the instrument canbe used for testing acuity, independent of the refractive system of theeye, over a wide range of illumination. In testing the color sense, thefilters 49 are suitably colored. By using a viewing aperture ofsubstantially 1.5 millimeters in diameter the results are renderedindependent of the refractive sys-. tem of the eye under test. Throughthe use of our optical system for focusing the light in the pupil of theeye, no light is wasted and hence ample range of intensity can beprovided by. a single light source. Changes from pre-exposure fields toa test field can be effected with a mini- 1 mum amountof time. Theinstrument can be conveniently operated in a darkened room since thescales are transilluminated.

Various modifications can obviously be made without departing from thespirit of our invention.

We claim:

1. An ophthalmic instrument for testing light sense comprising a closedcasing having a viewing aperture, means within said casing forselectively and successively providing illuminated pre-exposure and testfields, means for directing all of the light in' said fields into an eyeplaced at said aperture and means for measuring the amount of lightwhich enters the eye.

2. An instrument of the type described comprising a casing having aviewing aperture, a light source within said casing, lens means forimaging said source at the pupil of an eye positioned at said apertureand means for selectively positioning a diaphragm adjacent to said lensmeans to limit the size of field.

3. An instrument of the type described comprising a casing having aviewing aperture, a light source within said casing, means for varyingthe intensity of said source, lens means for imaging said source at thepupil of an eye placed at'said aperture, diaphragm means adjacent tosaid lens means for limiting the size of field and means for indicatingthe amount of light which enters the eye.

' 4. An instrument of the type described comprising a casing having aviewing aperture at one end thereof, a light source mounted at the otherend of said casing, light difiusing means mounted between said sourceand aperture, means for varying the intensity of illumination on saiddiffusing means and lens means for collimating light rays from saiddiffusing means and focusing them substantially at said aperture.

5. An instrument of the typev prising a casing having a viewing apertureat one end thereof, a light source mounted at the other end of saidcasing, light difiusing means mounted in said casing between saidsource-and aperture in position to receive light rays from said source,means for varying the illumination on said diffusing means, len's meansfor collimating light rays from said diffusing means and focusing themsubstantially at said aperture and means for selectively positioning adiaphragm adjacent to said lens means to limit the size of field.

6.An' instrument of the type described comprising a casing having aviewing aperture, a light source movably mounted at the other end of thecasing, a light diffusing member positioned between said aperture andlight source, means for imaging said member on an eye placed at saidaperture, and means for varying the illumidescribed com nation on saiddiffusing member, said last named means comprising mechanism for varyingthe distance between said source and member and light modifying filterspositioned between said source and member.

'7. An instrument of the type described comprising a casing, means forproviding an illuminated field within said casing and means on saidcasing for selectively holding either an apertured eye piece or achecking unit in position to receive light rays from said field, saidunit comprising means for checking the illumination of said field withthe illumination of a standard light source.

8. An instrument of the type described comprising a casing having aviewing aperture, a

single light source mounted at the other end of the casing, a lightdiffusing member positioned between said source and aperture, means forimaging said member at the pupil of an eye placed at said aperture andmeans for varying the intensity of illumination on said member, saidlast named means comprising two lenses positioned between said sourceand member and a diaphragm positioned between said lenses.

9. An instrument of the type described comprising a casing having aviewing aperture, a light source at the other end of said casing, a

light diffusing member positioned between said source and aperture,means for imaging said member at the pupil of an eye placed at saidaperture and means for varying the intensity of illumination on saidmember, said means comprising lens means positioned between said sourceand member and diaphragm means positioned adjacent to said lens means.

10. In an instrument of the type described the combination of a housing,means within said housing for providing an illuminated field, means forvarying the illumination on said field, a casing, means within saidcasing for providing an illuminated field in juxta-position to saidfirst named field and means for viewing the two juxta-posed I fields,said last named means comprising lens means and adjustable diaphragmmeans for selectively limiting the size of field.

11. A light sense tester having in combination means for producing twocontiguous illuminated fields, means for varying the illumination on oneof said fields, means for viewing said two contiguous fields anddiaphragm means for selectively varying the portion of said fields whichare visible through said viewing means.

CLARENCE ERROL FERREE. GERTRUDE RAND FERREE.

